vsprintf.c: add UTF-16 string (%ls) support

This is convenient for efi_loader which deals a lot with UTF-16.  Only
enabled with CC_SHORT_WCHAR, leaving room to add a UTF-32 version when
CC_SHORT_WCHAR is not enabled.

Signed-off-by: Rob Clark <robdclark@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Simon Glass <sjg@chromium.org>

examples/api/Makefile

@@ -34,6 +34,7 @@ EXT_COBJ-y += lib/div64.o
 EXT_COBJ-y += lib/string.o
 EXT_COBJ-y += lib/time.o
 EXT_COBJ-y += lib/vsprintf.o
+EXT_COBJ-y += lib/charset.o
 EXT_SOBJ-$(CONFIG_PPC) += arch/powerpc/lib/ppcstring.o
 ifeq ($(ARCH),arm)
 EXT_SOBJ-$(CONFIG_USE_ARCH_MEMSET) += arch/arm/lib/memset.o